Help with Absence Data Status

Use below Query where ReportMonth is a parameter to store your reporting month.

Solution Excel uploaded to https://1drv.ms/x/s!Akd5y6ruJhvhuUUKb3_p1vZ7Cp5C?e=eHE291 

let
    Source = Excel.CurrentWorkbook(){[Name="Table1"]}[Content],
    #"Changed Type" = Table.TransformColumnTypes(Source,{{"Personnel Number", type text}, {"Absence Start Date", type date}, {"Absence End Date", type date}}),
    #"Added Custom" = Table.AddColumn(#"Changed Type", "Status", each if [Absence End Date]=Date.EndOfMonth(#date(Date.Year([Absence End Date]),ReportMonth,1)) or (Date.Month([Absence Start Date])<>ReportMonth and Date.Month([Absence End Date])<>ReportMonth) then "All Month" 
else if Date.Month([Absence Start Date])=ReportMonth then "Commenced"
else if [Absence End Date]<=Date.AddDays(Date.EndOfMonth(#date(Date.Year([Absence End Date]),ReportMonth,1)),-1) and [Absence End Date]>=#date(Date.Year([Absence End Date]),ReportMonth,1) then "Returned"
else null)
in
    #"Added Custom"